1. Field of the Invention
This invention relates to a compact 4-chamber gas meter which provides the essential functions of a gas meter in a smaller volume, and, in particular, in a shallower depth, front to back. In particular, the gas meter of this invention comprises flag post to crankpost kinematics which provide good torque pulse characteristics within the constraints of a shallow meter box, valve drive kinematics which provide perfect coordination of valve timing with the ends of the strokes of the diaphragms of the gas meter, a lower box configuration which allows a molded plastic or die cast construction while accommodating rolling lobe diaphragms, and a valve plate with passages which accommodate a 4-chamber meter with parallel reciprocating valves.
2. Description of Prior Art
In a diaphragm-type gas meter, a quantity of gas is delivered through the reciprocation of measuring diaphragms by gas pressure. Generally, in this type of gas meter, the gas is introduced into a valve cage through an inlet port formed in the upper portion of the gas meter housing and alternately introduced into each measuring chamber formed in the lower portion of the housing through a distributing valve mechanism.
In a 4-chamber gas meter, the lower housing comprises two pairs of measuring chambers, each pair having a diaphragm which separates the measuring chambers. The motion of each diaphragm is controlled by a mechanism connecting that diaphragm to a crankpost. The mechanism and the crankpost, acting together, control the length of the stroke of each diaphragm and coordinate the timing of the stroke of each diaphragm to the stroke of the other diaphragm in the meter. Typically, an adjustment feature on the crankpost is provided to make small, precise changes to the length of the diaphragm stroke at the time of the final meter calibration. In some meters, temperature variations are compensated for by employing a bi-metallic device on the crankpost which varies the length of the stroke of the diaphragms in direct proportion to the absolute temperature of the gas being metered.
Each diaphragm has a corresponding valve in the meter. Valve opening is timed to begin to admit gas to the chamber on one side of the diaphragm when the diaphragm's position is approaching its minimum volume. The valve is timed to begin to exhaust gas from the chamber when the diaphragm is approaching the maximum volume of that chamber.
The timing of the valves is coordinated to the volume of the chambers by a mechanism that connects each valve to the crankpost. Typically, an adjustment feature on the crankpost for making small, precise changes to the valve timing at the time of final meter calibration is used. This adjustment allows for the advancement or retardation of the valve movements. Gas volume is measured by counting the revolutions of the crankpost. This is accomplished by a geared connection between the crankpost and a mechanical counting means.
Diaphragm meters of the type discussed hereinabove generally are taught by U.S. Pat. Nos. 4,091,668; 3,589,189; 3,587,315; 3,415,121; 3,261,206; 3,161,049; 2,932,198; 2,818,046; 2,741,122; 2,667,147; 2,663,189; 2,544,665; 2,367,735; 2,346,229; 2,313,515; 2,296,485; 2,296,476; 2,281,671; and 2,223,555.
Designing a 4-chamber gas meter which is compact, that is, having a small front-to-back dimension compared to traditional meters, requires the design of crankposts and valve drive mechanisms which overcome the kinematic problems associated with compact 4-chamber gas meters. U.S. Pat. No. 4,091,668 teaches a diaphragm-type gas meter having one crank plate on which a pair of diaphragm movement transmission levers are mounted and a second crank plate on which a pair of valve actuating levers which overlap each other rockably around the central axis of a crank shaft are pivotally mounted. The valve actuating levers are connected to a pair of valve members which reciprocate over a fixed angular range according to the rotation of a crank mechanism. U.S. Pat. No. 2,663,189 teaches a gas meter having two diaphragms operating flag rods disposed at diagonally opposite points in a plan view of the meter mechanism, each flag rod operating a gas transfer valve in such a way that the valve has a movement in an arc of a circle with the flag rod as its axis, and each valve being relatively long in a direction radial to the flag rod axis with its transfer passage in the said radial direction. U.S. Pat. No. 2,367,735 teaches a 4-chamber gas meter in which valves communicate with each main chamber through faces of the chamber which are not parallel to the diaphragm. U.S. Pat. No. 2,346,229 teaches a 4-chamber gas meter in which each diaphragm oscillates a spindle carrying an arm, the two arms rotating a crank spindle by which valve covers disposed parallel to each other are oscillated between the front and back of the meter along the same axis. And, finally, U.S. Pat. No. 3,589,189 teaches a 4-chamber gas meter having a pair of slide valves, operated by a valve actuating mechanism pivotally connected to a single throw crank in a manner which advances the valve timing to permit greater accuracy at higher volumes of flow.
A 4-chamber meter produces the most uniform driving torque from the diaphragms to the crankpost if the motion of the two diaphragms is essentially 90.degree. out of phase. It is also highly desirable that the motion of the two diaphragms is delivered to the crankpost through a common crankpin. So doing allows the stroke adjustment to be uncomplicated while still influencing the length of both diaphragm strokes. It is also desirable that the links which connect the flag arms to the crankpin have a substantially greater length than the diameter of the crankpin motion. So doing helps to further improve the uniformity of driving torque. It is also desirable that each stroke of each diaphragm, where the inward motion of a diaphragm is a stroke and the outward motion is another stroke, occur over 180.degree. of crankpost rotation. In this way, a valve drive mechanism can be designed which assures the valve timing is equally coordinated to the ends of all four diaphragm strokes. None of the prior art references of which we are aware teaches a crankpost and valve drive mechanism which satisfies these criteria within a compact 4-chamber gas meter.